1. Field of the Invention
The present invention relates to a printer. More particularly, the invention relates to a printer which is compact, can accurately supply paper and has reduced noise characteristics. Additionally, the printer enables easy recovery from the paper jams and can be selectively operated in various modes according to the user's preference.
2. Background Art
The following is a discussion concerning a conventional paper supply mechanism and considerations in designing such a mechanism. In designing desk-top printers, one of the major objects is to minimize the space occupied by the printer. In particular, in the case of small printers of this type, it is desired to reduce the size of the printer to be approximately the same size as the paper. For this reason, design freedom of the paper transport path is limited to provide such a layout that a recording paper is taken out of the placing position at an acute angle. Accordingly, when the paper has been conveyed toward the platen, conveyance of the paper is impeded by the paper supply rollers, so that the paper supply rollers must be displaced to a dislocated position (i.e., to a "no paper feed" position). To transport the paper to the print stage without any skew in the paper, as described in Japanese Patent Publication No. Sho. 58-6637 or 62-39261, it is necessary to use the device for causing the paper to bend at a position of this side of the platen to thereby correctly positioning the paper with respect to the platen with a self-restoring force of the paper, by rotating the platen reversely while the paper abuts against the platen or by once nipping a leading edge of the paper in the platen and thereafter rotating the platen reversely to return back the leading edge of the paper out of the platen.
Considerably complicated mechanisms are required for dislocating the paper supply rollers and for rotating the platen in the forward and reverse directions. Japanese Patent Laid-Open Publication No. Hei. 3-244569 discloses a technique where an intermittent motion gear is cyclically driven so as to supply the paper. Japanese Patent Publication No. Hei. 1-184174 discloses a technique where a one-way clutch is driven when the carriage is moved to the paper feed position so as to supply the paper. However, each of these techniques does not provide a power transmission means on the carriage.
In the case that these discharged techniques are applied to the small size printers, it is impossible to reduce the size of the printer, and the cost to manufacture the printer is increased. Attempts to minimize the size of the printer without using such a power transmission mechanism have resulted in poor paper supply characteristics (i.e., unsmooth paper supply).
Japanese Laid-Open Patent Publication No. Hei. 2-295837 discloses a paper supply mechanism using a planetary gear mechanism. The paper supply mechanism is not provided with a stopper for suppressing an excessive swing motion of the paper supply rollers. As a result, the paper supply rollers excessively press against the paper, thereby forming wrinkles in the paper.
The following is a discussion of a conventional paper transport mechanism. FIG. 38 is a schematic view showing an example of a printer. In the figure, a paper supply roller 1 functions to individually supply recording papers P from a cassette 2 containing the paper. The supplied paper P is guided by a paper guide 4, and conveyed around a platen 5. The paper P is also transported while being nipped between two hold rollers 6 and the platen 5. After being conveyed past print head 7 for printing thereon, the paper P is discharged through an exit 8. The hold rollers 6 are mounted on a holder 6a which is attached through a compressed spring 6b to a base frame 9. With the paper transport mechanism thus constructed, the hold rollers 6 and the platen 5 cooperate to nip the paper P therebetween and to convey the paper forward.
One of the possible approaches for reducing the size of the printer thus constructed is to locate the cassette 2 within the main body of the printer. One example of such an approach is illustrated in FIG. 38 wherein the paper supply roller 1' and the cassette 2' are disposed as indicated by phantom lines.
During the paper feeding operation, rotation of the paper supply roller 1 is temporarily stopped after the paper P moves forward a preset distance. In this case, the paper supply roller 1 tends to prevent conveyance of the paper by the interaction of the platen 5 and the hold roller 6. Specifically, when the paper supply roller 1 is located at the position indicated by phantom line 1' resting on the paper P', tension generated in the paper P' acts to urge the paper in the direction of arrow a tending to reduce the pressure applied by the hold roller 6 against the platen 5. As a result, a pressure force (i.e., a paper moving force) fb applied by the roller 6 against the platen 5 is reduced thereby preventing accurate conveyance of the paper.
A further problem associated with the conventional printer is the jamming of the paper. Referring to FIG. 38, a case C of the printer consists of a main body case C1 and a cover case C2. The cover case C2 is rotatable between open and closed positions with respect to the main body case C1. If a paper jam occurs at a position A2 downstream of printing stage A, a user can open the cover case C2 and remove the jammed paper.
Position A1 upstream of the print stage is covered with the main body case C1. Further, the paper guide 4 is fastened to the main body case C1 by means of a screw 4a. Accordingly, it is difficult to remove the jammed paper at the position A1. If a user attempts to pull the end of the paper in an effort to remove the jammed paper, the paper will frequently tear resulting in the user being unable to remove the remaining piece of paper disposed at position A3 near the hold rollers. To remove it, a service man must be called.
Designs which allow the user to remove the jammed paper disposed at positions upstream and downstream of the printing position are disclosed in Japanese Utility Model Laid-Open Publication No. Sho. 63-7548 and Japanese Patent Laid-Open Publication Nos. Hei. 2-297469 and 2-69273. In the construction of these printers, the print mechanism or the paper transport mechanism is removed or opened to enable the jammed paper to be removed. However, repeated removal or opening of these mechanisms will adversely effect the mechanisms.
An example of the cassette is shown in FIGS. 39(a) and (b). A cassette body 11 contains a number of papers P. A pair of peel-off claws 13 individually remove papers from the stack of papers and supply them in a forward direction. A hopper 14 urges the paper P upwardly such that the corner edges 12a thereof abut against the peel-off claws 13. The hopper 14 is assembled into the body 11 by inserting the forward portion of the hopper, having a curved end 14a, into an opening 11a in the body 11 until the curved end 14a engages a protruding piece 11b of the body 11. As a result, the hopper 14 can pivot within a limited range about the engaging point of the curved end 14a with respect to the protruded piece 11b. A spring 15, provided between the rear portion of the hopper 14 and the body 11, acts to urge the hopper, and attendantly the stack of paper P, upwardly.
The cassette, containing the paper stack P, is loaded into the printer body. Thereafter, the printer is turned on resulting in the paper supply roller 16 rotating in the direction of an arrow A. Correspondingly, the uppermost sheet of paper is conveyed in the direction of arrow B causing the corner edges 12a and 12a of the paper to abut against the peel-off pawls 13 and 13 so that the sheet is curved upwardly. At the instant that the progressive curving of the paper reaches a critical point, the corner edges 12a and 12a are released from the peel-off pawls 13 and 13, so that the uppermost paper is separated from the underlying paper, and is moved forwardly. In the cassette thus constructed, the peel-off pawls 13, provided separately from the cassette body 11, are secured to the body 11 in such a manner that after the hopper 14 is mounted in the manner discussed above, a pin 13b protruded from the underside of a mounting piece 13a is inserted through an elongated hole 11c of the body 11 and is properly positioned. Thereafter, the mounting piece is fastened to the body 11 by means of a fastening piece 13c.
Due to such a construction where the peel-off pawls 13 are independent of the cassette body 11, it is difficult to improve the positioning accuracy of the cassette with respect to the paper supply roller 16 to achieve the best paper separation performance.
Further, in the case where the peel-off pawls 13 and the cassette body 11 are formed as a unitary construction, it is impossible to secure the hopper 14 to the cassette. That is, in the process of engaging the protruded piece 11b of the cassette body 11 with the curved end 14a of the hopper 14 through the opening 11a, the lower side of the corners 14b of the hopper 14 would abut against the upper sides 13d of the peel-off pawls 13 and 13.
The following is a discussion of the paper discharge mechanism and tractor in reference to a second example of a printer, as illustrated in FIG. 40.
As shown, a discharge roller 28, disposed downstream of platen 20, is forcibly fitted around a roller shaft 22, which is supported by a frame member 21. The discharge roller 28 receives a drive force transmitted through a gear (not shown) fixed to the end of the roller shaft 22.
After printing, a cut paper P1 is lifted due to a friction force by the discharge roller 28 past the discharge cover 24. A discharge spring 23 formed with a thin resin is provided in order to force the cut paper P1 into the printed paper container.
A tractor 27 is disposed upstream of the printing stage for conveying continuous paper P2. Tension must be constantly applied to the continuous paper P2 in order to secure the proper pitch of the continuous paper P2. To this end, the peripheral speed of the discharge roller 28 is set to be higher than that of the platen 20.
FIG. 41 is a sectional view of a tractor release mechanism in a friction condition where the cut paper P1 is pressed against the platen 20, and is conveyed forwardly in cooperation with paper hold rollers 26a and 26b. The hold rollers 26a and 26b are pivotally supported by a holder 36. A paper hold lever 37 is attached to a release shaft 38 supported by a frame 31 of the printer body. A coiled spring 39 is placed on the frame 31. The coiled spring 39 urges the roller holder 36 upwardly through the paper hold lever 37. As a result, the hold rollers 26a and 26b contact the platen 20, thereby generating a pressure force against the platen.
FIG. 42 is a sectional view of a tractor release mechanism in a state where the cut paper P1 is detached from the platen 20, and a continuous paper P2 is supplied from the tractor 27 into the printer body.
When a release lever (not shown), attached to the release shaft 38, is turned to a release position, the release shaft 38 and the paper hold lever 37 both pivot in the direction of arrow A, while resisting the urging force of the coiled spring 39. The roller holder 36 moves downwardly and the hold rollers 26a and 26b separate from the platen 20. A release state is set up in the mechanism. Thus, the paper hold lever 37, the release shaft 38, and the release lever (not shown), which make up the tractor release mechanism, are mounted on the frame 31 of the printer body.
As described above, in the second example of the conventional printer, the frame member 21, the roller shaft 22, a chain of gears (not shown), and the discharge spring 23 are required for the paper discharge mechanism. Therefore, there are an excessive number of parts requiring a correspondingly long assembly time and resulting in an increased cost. When the leading edge of the paper abuts against the discharge spring 23, the spring acts as a load. As a result, the pitch of the paper is not uniform. Further, relatively loose contact of the paper occurs, generating a noisy printing sound.
When only the printer body, absent the tractor 27, is operated to print visual information on a cut paper P1, the paper hold lever 37, the release shaft 38 and the release lever, which form the tractor release mechanism, are not used. Further, the number of parts of the printer body is increased resulting in an increase in the cost of manufacturing and the size of the printer.
Japanese Patent Laid-Open Publication No. Hei. 3-200660 discloses a printer using a planetary gear for the drive force transmission mechanism of the discharge roller. In this printer, since the planetary gear, which does not directly contact the platen, is used for the intermediate transmission mechanism, the mechanism is complicated.
Recently, to reduce the space occupied by the printer, the printer is placed in various different positions. For example, the printer of FIG. 40 is generally positioned in an upright manner with the rear side 41 of the printer acting as the bottom surface.
Reduction of noise generated by the printing head 42, particularly the wire dot head, has also been desired in this technical field. Most of the sound generated by the printing head 42 during operation is discharged through a discharge port 49 and a discharge path 48. To reduce the noise, it is desirable to form the discharge port in the rear side 41 of the printer. However, positioning the printer in this manner creates problems in that access to the printed paper is poor. Thus, use of the printer in the upright position is not practical.
The following is a discussion of the tray for receiving discharged papers. In the printer shown in FIG. 40, a paper P1 is stored on the tray 51 with the printed side facing upwardly. In such printers, a user can read the printed material when the paper is being discharged. However, the user must rearrange the papers in a reverse order when the user removes the set of printed papers from the tray. In some known printers, the printed paper is stored with the printed side facing downwardly. In the printer which stores the paper in a downwardly facing manner, there is no need of reversely ordering the set of papers.
To overcome these problems, printers which allow the printed papers to be selectively stored facing upwardly or downwardly have been proposed in Japanese Patent Laid-Open Publication No. Hei. 3-200660, Japanese Patent Laid-Open Publications Nos. Sho. 64-81758, Sho. 63-101256 and Japanese Utility Model Laid-Open Publication No. Hei. 2-103053.
Each of these printers employs a turning mechanism to turn the discharge tray for selecting the upward-facing or downward-facing state of printed papers. However, the turning mechanism requires complicated structure and leads to increase in the size of the printer.
The following is a discussion concerning the paper feed path of conventional printers. There is a known printer which makes the environmental setting by communication with the user in the following manner. In this type of printer, the printer prints a message to the user on a paper, and transports the paper with the printed message up to a position where the user can read it. Then, the printer retracts the printed paper, and prints another message on the paper, and transports again the printed paper to that position. In this way, the use environment of the printer is set.
In this type of the printer, the printed paper must be transported until it is discharged from the discharge port to a position where the user can read the printed message, and then the printed paper must be retracted. Therefore, the return path of the printed paper is relatively long resulting in an increase size of the printer.
A principle object of the invention is to provide an printer which is compact, can accurately supply paper and has reduced noise-characteristics. Additionally, an object of the invention is to provide a printer which enables easy revery from paper jams and can be selectively operated in various modes according to the user's preference.